The acute dose-response relation between the amount of dietary cholesterol fed and the amount absorbed was studied during two test meals in 18 normal subjects. Pentadeuterated cholesterol was given orally to quantitate intestinal cholesterol uptake and hexadeuterated cholesterol was given intravenously to measure dilution of the absorbed cholesterol in body pools. The tracers were detected in plasma cholesterol after 4 days by gas chromatography/negative ion mass spectrometry. Baseline cholesterol absopriton in the presence of 26 mg cholesterol tracer was 40.7(2.3%. This decreased by 4.9 percentage points (p=0.05) when a total of 188 mg cholesterol was included in the meal and by 15.6 percentage points (p=0.006) when 421 mg holesterol was given, showing that the efficiency of cholesterol absorption declines appreciably even with moderate increases in cholesterol dose. Considerable variation was noted in the response of different subjects and on the higher chol esterol do se dietary cholesterol absorption varied 5.3-fold from 40 mg to 212 mg. Fasting plasma insulin was correlated with the ability to absorb higher cholesterol doses without loss of efficiency (rs=0.700, p=0.036). Absorption of an acute dietary cholesterol load is variable and declines on average over common levels of cholesterol intake.